L.F.N.D. Carramate
University of Aveiro
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Featured researches published by L.F.N.D. Carramate.
Journal of Instrumentation | 2011
L.F.N.D. Carramate; C. A. B. Oliveira; Augusto Silva; A. Da Silva; J.M.F. dos Santos; J.F.C.A. Veloso
In the present work a new system for Quantum Computed Tomography was developed and tested, envisaging its application to small animals and mammography imaging. It consists of a Micro-Patterned Gas Detector based on the Micro-Hole and Strip Plate, operating in single-photon counting mode. The Micro-Hole and Strip Plate allows the storage of the position of interaction and the energy information of each single X-ray photon. With this information it is possible to select the energy range to reconstruct the images of cross sections, enabling the enhancement of different structures according to their attenuation coeficients. It is also possible to use the energy information to weight each photon in the sinogram construction. In the present work we consider three types of weighting factors giving rise to three different types of images, namely Integrating, Counting and Energy Weighting Technique (EWT). For each CT acquisition the system allows us to construct any of these types of images without the need for extra measurements. Some features of the CT image improve with the application of the Energy Weighting Technique, namely the Signal-to-Noise Ratio (SNR), the image Contrast, and the Contrast-to-Noise Ratio (CNR). The maximum contrast enhancement was about 23%, the maximum SNR improvement was about 22% and the maximum CNR improvement was about 31% between integrating and EWT images.
Journal of Instrumentation | 2016
C.D.R. Azevedo; P.M.M. Correia; L.F.N.D. Carramate; Aniceto Silva; J.F.C.A. Veloso
Discrepancies between the measured and simulated gain in Thick Micropatterned gaseous detectors (MPGD), namely THGEM, have been observed by several groups. In order to simulate the electron avalanches and the gain the community relies on the calculations performed in Garfield++, known to produce differences of 2 orders of magnitude in comparison to the experimental data for thick MPGDs. In this work, simulations performed for Ne/5%CH4, Ar/5%CH4 and Ar/30%CO2 mixtures shows that Garfield++ is able to perfectly describe the experimental data if Penning effect is included in the simulation. The comparison between the number of excitations which may lead to a Penning transfer, is shown for THGEM and GEM, explaining the less pronounced gain discrepancies observed in GEM.
Journal of Instrumentation | 2013
Aniceto Silva; C.D.R. Azevedo; L.F.N.D. Carramate; Tarcila Bretas Lopes; I.F. Castro; R. De Oliveira; J.F.C.A. Veloso
A new X-ray imaging detector based on a 2D-THCOBRA micropatterned structure using a simple position readout is proposed. It consists of a hybrid device that combines the prop- erties of a THGEM and a 2D-MHSP in a single structure, having two charge multiplication stages reaching the demanded gains for the use of charge division readout methods. For position determination, the new 10 10 cm 2 2D-THCOBRA structure uses two orthogonal resistive lines located at the end of the anode and top electrodes. The charge signal pulses collected at the end of each resistive line are digitized and processed in order to determine the center-of- gravity of the electron avalanche distribution. The detector uses a preamplification stage performed by a THGEM, followed by the 2D- THCOBRA, being operated in Ne/5%CH4 at atmospheric pressure. A characterization of the de- tector in terms of charge gain was made as a function of the voltage applied to the electrodes of the 2D-THCOBRA structure. The energy resolution of the system was also measured, envisaging Energy Weighting Technique (EWT) applications. The system characterization in terms of spatial resolution is presented together with imaging examples to evaluate its performance in X-ray imaging applications.
Journal of Instrumentation | 2013
Tarcila Bretas Lopes; Aniceto Silva; C.D.R. Azevedo; L.F.N.D. Carramate; D.S. Covita; J.F.C.A. Veloso
In this work, a new position sensitive gas photomultiplier (GPM) based on a cascade configuration is proposed. The GPM is composed by two THGEMs, followed by a 2D-THCOBRA being operated in Ne/CH4(5%), at a pressure of 1 bar in VUV single photon mode. The 2D-THCOBRA is a hybrid microstructure which combines the benefits of a THGEM and a 2D-MHSP, presenting two independent charge multiplication stages. The position capability is performed by using two orthogonal resistive lines crossing each one the readout electrodes. The position is obtained by measuring the charge sharing in both ends of each resistive line, by using only 2 readout channels. This work focuses the study of the detector gain, Ion Back Flow (IBF) and spatial resolution. A charge gain of 106 and an Ion Back Flow (IBF) values of about 20% were measured. Position resolutions below 300 μm (FWHM) were obtained for single VUV photon counting mode operation.
IEEE Transactions on Nuclear Science | 2010
C.A.B. Oliveira; C. A. Santos; L.F.N.D. Carramate; Augusto Silva; Natal da Luz; J.M.F. dos Santos; J.F.C.A. Veloso
The 2D-MicroHole and Strip Plate (MHSP) is a simple single photon counting detector for X-ray imaging. It is a micropattern gaseous detector having two orthogonal resistive lines crossing the amplification and readout electrodes on both sides of the MHSP for position detection. In this detector, not only the interaction position can be determined, but also the energy of individual photons. The detector energy resolving capability offers the possibility of obtaining three types of images of the intensity distribution: Integrating, Counting and Energy Weighting. In the first case, the intensity of each pixel is obtained by adding the energy of each event; in the second case, by counting the number of events and; in the third case, by adding each event weighted by a factor that depends on its energy. When a PVC step phantom is irradiated with a 20 kV copper anode X-ray tube, the results show a Contrast Enhancement up to 6% when Counting and Integrating images are compared and up to 20% when comparing Energy Weighting and Integrating images. A biological sample, a common quail wing, was also imaged. Studies of the Contrast Enhancement and image quality between different techniques as a function of energy windows are present.
Journal of Instrumentation | 2016
C.D.R. Azevedo; D. González-Díaz; P.M.M. Correia; S. Biagi; Aniceto Silva; L.F.N.D. Carramate; J.F.C.A. Veloso
A study of the effect of gas pressure in the position resolution of an interacting X or γ-ray photon in a gas medium is performed. The intrinsic position resolution for pure noble gases (Argon and Xenon) and their mixtures with CO2 and CH4 was calculated for several gas pressures (1–10 bar) and for photon energies between 1 and 60 keV, being possible to establish a linear relation between the intrinsic position resolution and the inverse of the gas pressure in the indicated energy range, as intuitively expected. We show how, at high pressures and low photoelectron energies, this intrinsic 1/P scaling is modified due to the diffusion of the primary ionization in the direction perpendicular to the electric field. In order to evaluate the quality of the method here described, a comparison between the available experimental data and microscopic simulations is presented in this work and discussed. In the majority of cases, a good agreement is observed. The conditions to achieve position resolutions down to 10 μm in a realistic detector are shown and discussed.
Journal of Instrumentation | 2013
L.F.N.D. Carramate; Frank Nachtrab; M Firsching; Augusto Silva; A. Da Silva; J.F.C.A. Veloso; N Uhlmann
Energy resolved imaging has been possible with a newest generation of radiation detectors with photon counting and spectroscopic capabilities. This innovation gives the possibility to enhance the image quality by applying techniques using the energy information. In this work two X-ray Computed Tomography (CT) Systems were assembled with two different energy resolving detectors: Medipix2 and MicroHole & Strip Plate (MHSP). These detectors have the aforesaid characteristics and showed a good performance for X-ray imaging. The Energy Weighting Technique (EWT) and Basis Material Decomposition (BMD) techniques were applied with good results. An improvement of 31% in the CNR was achieved by applying the EWT in the MHSP data and, using Medipix2, two basis materials (Carbon based and Aluminium) were decomposed successfully with densities close to the real values.
nuclear science symposium and medical imaging conference | 2012
Aniceto Silva; C.D.R. Azevedo; L.F.N.D. Carramate; Tarcila Bretas Lopes; R. De Oliveira; J.F.C.A. Veloso
A new x-ray imaging detector based on a THCOBRA micropatterned structure using simple position readout is proposed. It consists on a hybrid device that combines the properties of a THGEM and a 2D-MHSP in a single structure, having two charge multiplication stages allowing to reach the high gains needed to use resistive line readout methods. The new THCOBRA structure has a 10×10 cm2 sensitive area and uses two orthogonal resistive lines located at the end of the electrodes in both sides of the structure for position sensitivity. The charge is collected in the end of each resistive line being the resulting signals digitized and processed. Therefore, from the amplitude of each pair of signals it is possible to determine center-of-gravity of the electron avalanche distribution. The detector uses a preamplification stage performed by a THGEM, followed by the THCOBRA, being operated in Ne/5%CH4 at atmospheric pressure. The energy resolution of the system was measured envisaging Energy Weighting Technique (EWT) applications. The system characterization in terms of spatial resolution is presented together with imaging examples to evaluate its performance in X-ray imaging applications.
Journal of Instrumentation | 2015
L.F.N.D. Carramate; Aniceto Silva; C.D.R. Azevedo; D.S. Covita; J.F.C.A. Veloso
Photon counting detection with energy resolution and the consequent possibility to improve image quality become possible with the development of energy resolved detectors. The 2D-Thick-COBRA (2D-THCOBRA), a recently introduced MicroPattern Gaseous Detector (MPGD), with an active area of 10 × 10 cm2, specially designed for imaging purposes allows to determine the interaction position and also the energy of each single photon reaching the detector. In this work, the performance of a single 2D-THCOBRA operating in Ne/CH4 (95/5) (at 1 bar) is presented based on studies of charge gain, energy resolution, count rate, stability and spatial resolution. The detector shown a very stable operation allowing for gains of about 104. An energy resolution of 22% for 8 keV, count rates up to 1 × 106 Hz/mm2 and a spatial resolution of about 1.2 mm were achieved with this detector. Some examples of X-ray transmission imaging of some biological samples are also shown.
Journal of Instrumentation | 2012
L.F.N.D. Carramate; C. A. B. Oliveira; Aniceto Silva; A. Da Silva; J.M.F. dos Santos; J.F.C.A. Veloso
The present work reports a new system for Computed Tomography (CT) with Multi- Slice (MS) capability using the 2D-MicroHole & Strip Plate (MHSP) detector. The system is based on the third generation of CT scanners and includes a MHSP based detector which achieves gains above 10 4 and has the capability to discriminate the interaction position of the incoming radiation in 2D. The possibility of operating in single photon counting mode with energy discrimination allows the selection of energy ranges for image reconstruction and the application of the Energy Weighting Technique (EWT). The EWT improves the image contrast and the Signal to Noise Ratio of the images. The reconstruction of three-dimensional images of a PMMA phantom with holes filled with chalk and air or brass are shown as a good representation of the studied objects.